In recent years, designing has been accomplished by using the Computer Color Graphic (CG) system for a wide range of industrial fields including fashion, automobiles, household electric appliances, printing and many other industries. The CG system is used not only to create images of schematic color designs but also to determine the final design colors accurately. Technology is necessary for accurately transmitting the light-source color, which is perceived and determined on the color CRT monitor of the CG system by the designer, to the production field as an equivalent non-luminous object color or data.
According to the prior art, for transmission of color on a color CRT monitor, a hard copy or photographic copy of the color on the color CRT monitor is prepared by a special camera or ink jet printer. The toning field operations, such as the Computer Color Matching (CCM) operation, are accomplished based on non-luminous object color data, a spectral reflectance factor or the CIE tristimulus values, which are obtained by colorimetry.
In this case, however, the light-source color data is transformed to non-luminous object color data by using the hard copy as a color transmission medium. Unfortunately, the hard copy cannot accurately reproduce the color perceived on the CG system by the designer because spectral characteristics of the phosphors of the color CRT monitor are fundamentally different from those of the ink or photographic coloring agent used in production of the hard copy. This means that the transformation from light-source color data to non-luminous object color data is seriously inaccurate, and that the step from the design stage to the toning field stage, using the CG system and the CCM, cannot effectively and accurately be achieved.
Therefore, the present procedure is hampered by inaccuracy in the color transmissions taken from the hard copy. From this embarrassing situation, the technology that allows the light-source color on the CG system determined by the designer to be transformed to non-luminous object color data directly from the CG system without using an intermediate medium, such as a hard copy, has come to be noted.
The technology involved in not using a color transmission medium uses a transformation formula for transforming the video drive signals of the color CRT monitor into the CIE tristimulus values X, Y, and Z (i.e., non-luminous object color data). (Journal of Imaging Technology, Volume 13, Number 4, August 1987).
In order to determine the transformation formula between the RGB video drive signals and the CIE tristimulus values of the non-luminous object color, according to the prior art thus far described, the chromaticity coordinates of a white light-source color in the white balance of the color CRT monitor is used as a parameter for determining the undetermined coefficients of the transformation formula.
However, this technology is accomplished in a situation which is absolutely different from that of a practical CRT observation, in which only one light-source color emitted over the entire color CRT monitor is observed in a dark room which inhibits perception of the surroundings of the color CRT monitor. A standard white light (i.e., the light having chromaticity coordinates coincident to those of the white balance) illuminating only the object placed in the vicinity of the color CRT monitor is prepared. The illuminance of the standard white light is adjusted so that the white light-source color on the color CRT monitor and the unreal, perfected reflecting diffuser are coincidentally perceived in brightness. Thus, the technology mentioned here is difficult to put into practical use.